Digital cameras have become pervasive in photography since their commercial introduction in the 1990s. In fact, many camera manufacturers have ceased production and/or development of conventional film cameras and focused entirely on digital models. Digital cameras provide various conveniences over film cameras that have increased their popularity. For example, digital cameras provide images that are readily downloadable and printable without requiring a photo lab. In addition, digital cameras generally include a liquid crystal display that provides instant feedback as to the image quality. Furthermore, digital cameras allow a user to experiment and view the outcome without the expense of exhausting film supply. If a digital image is found undesirable it may be deleted and a new image may be recorded in its place. Digital cameras also allow the user to change film speed without being required to change the recording media. In a film camera, the film speed may only be changed by replacing the film with film having the desired film speed.
An image sensor is used in digital cameras in place of film to record an image that is projected into the camera. The image sensor is generally a charge-coupled device (CCD) or a complimentary metal-oxide semiconductor (CMOS) sensor that is built into the camera body during manufacture.
Those sensors are oftentimes exposed to dust particles, especially when the camera is a digital single-lens reflex camera (DSLR) that is configured to receive replaceable lenses. However, dust particles incident on the sensor reduces image quality. Image sensors are not designed to be replaced so the exposure of the sensor to dust requires sensor cleaning. Cleaning the image sensor exposes the sensor to the risk of damage so manual sensor cleaning is preferably undertaken only when sensor contamination has reached significant levels. Because of the size of dust particles and accessibility to the sensor, inspection of the sensor to determine the level of contamination is not a trivial task.
A common method of inspecting a digital camera sensor to determine the level of contamination is to take a picture of a uniformly illuminated surface. The image is taken with a small aperture setting, e.g., f/22-f/45 and with the lens focused on the closest focus setting. The image is then reviewed on a computer monitor to determine the level of contamination. Using that technique, dust particles on the sensor produce visible spots on the image. However, the image provides a map of the dust particles that is flipped 180 degrees from top to bottom. Based on that image a user may determine whether the contamination is substantial enough to require cleaning. It has also been suggested to utilize the same technique, but to manipulate the image with image editing software to improve the dust particle mapping.
Such methods present various disadvantages. One disadvantage of the method is that it requires access to a monitor to adequately view the image of the dust particles, but in many situations, such as when traveling, a monitor may not be available. In addition, if the user desires to target the dirtiest portions of the sensor, it requires the user to correlate the locations presented in the flipped image with the actual particle locations on the sensor. Furthermore, such a method does not clearly indicate whether the contaminants are on the sensor, a lens or a filter surface. A still further disadvantage is that if image processing is utilized, such software may not be available or requires special knowledge to adequately perform the processing steps.
In view of the above, there exists a need for a sensor inspection device that is compact and that does not require use of a monitor or image processing to perform the inspection.